1. Field of the Invention
This invention relates to a gyroscope and an input apparatus that uses the gyroscope, and more particularly relates to a gyroscope of the type that detects the displacement of a leg of a tuning fork particularly due to angular velocity input in the form of the capacitance change and an input apparatus that uses the gyroscope of this type.
2. Description of the Related Art
Heretofore, a gyroscope comprising a tuning fork consisting of conductive material such as silicon has been known. In the case of a gyroscope of this type, a leg of a tuning fork is vibrated in one direction, the vibration in the direction perpendicular to the above-mentioned vibration direction generated by Coriolis force is detected when the angular velocity round the center axis in the longitudinal direction of the leg is entered during vibration. Because the magnitude of the vibration generated by Coriolis force corresponds to the magnitude of the angular velocity, a gyrosensor is used as an angular velocity sensor, and for example, a gyrosensor is applied to a coordinate input apparatus or the like for a personal computer.
FIG. 33 is a diagram illustrating the structure of a tuning fork that is the main component of a conventional gyroscope. As shown in this diagram, the exemplary tuning fork 200 has three legs 201 and a support 202 that connects respective base sides of the legs 201, and consists of silicon that is rendered conductive. The tuning fork 200 is fixed on the base plate 203 by the support 202, and driving electrodes (not shown in the drawing) are provided respectively. under the legs 201. Therefore, when a voltage is applied on the driving electrodes, the legs 201 are vibrated in the vertical direction by electrostatic attractive force.
In the case of a gyroscope of this type, horizontal vibration is caused when angular velocity round the rotation axis in the longitudinal direction of the legs 201 is entered during vertical vibration, and the horizontal vibration is detected by use of a pair of detection electrodes 204 disposed on both sides of each leg 201. In detail, when a leg 201 is displaced in the horizontal direction, the gap between the detection electrode 204 disposed on one side of the leg 201 and the leg 201 is narrowed, the gap between the detection electrode 204 disposed on the other side of the leg 201 and the leg 201 is concomitantly widened, and as the result a pair of two electrostatic capacities formed by the detection electrodes 204 and the leg 201 changes. Based on the electrostatic capacity change, the magnitude of an input angular velocity can be detected.
In the case of a gyroscope having the structure described hereinabove, the narrow gap design between a leg 201 and adjacent legs 201 (referred to as inter-leg gap hereinafter) is limited because the detection electrodes 204 are disposed respectively on both sides of the legs 201. In detail, assuming that the width of a detection electrode 204 is denoted by x1, the gap between a detection electrode 204 and an adjacent leg 201 and a gap between adjacent detection electrodes 204 are denoted by x2, then an inter-leg gap G=2xc3x971+3xc3x972. Because of the working limit of x1 and x2 in silicon working by means of general semiconductor device fabrication technique, the narrow inter-leg gap G design has been limited.
On the other hand, it has been found that xe2x80x9cQ-valuexe2x80x9d, which is a performance index for representing the resonance magnitude of a device of this type becomes large if the inter-leg gap G of-a three-leg tuning fork is reduced. If Q-value could be made large, not only the detection sensitivity of angular velocity is expected to be improved but also the conversion efficiency from electric energy supplied to the device to vibration energy is expected to be improved, and thus the reduction of driving voltage will be reduced.
However as described hereinabove, though it is expected that the narrow inter-leg gap design is variously advantageous in miniaturization of a device, improvement of detection sensitivity, reduction of driving voltage, and the likes, the narrow inter-leg gap design has not been realized because the narrow inter-leg gap is limited in the case of the conventional gyroscope.
The present invention has been accomplished to solve the above-mentioned problem, and it is the object of the present invention to provide a high quality and low cost gyroscope that is variously advantageous as described hereinabove.
To achieve the above-mentioned object, the first gyroscope of the present invention is characterized by comprising a vibration member served as a tuning fork, a base material disposed so as to face to the above-mentioned vibration member, a driving means for driving the above-mentioned vibration member, a plurality of detection movable electrodes connected to each other in parallel and provided on the surface parallel to the displacement detection direction of the free end portion of the above-mentioned vibration member, each of which has a Width equal to or larger than the maximum amplitude in the displacement detection direction of the above-mentioned vibration member, and a plurality of detection fixed electrodes connected to each other in parallel and provided on the above-mentioned base material disposed so as to face to the above-mentioned plurality of detection movable electrodes and so as to form the capacitance between the above-mentioned plurality of detection fixed electrodes and the above-mentioned plurality of detection movable electrodes
The detection principle of the gyroscope of the present invention is based on the detection of the vibration of a vibration member of a tuning fork (equivalent to the xe2x80x9clegxe2x80x9d described hereinbefore) by means of capacitance change like the conventional gyroscope. Usually, the capacitance C is represented by the following equation.
C=xcex5xc2x7(S/d)xe2x80x83xe2x80x83(1)
(wherein xcex5 denotes the dielectric constant, S denotes the area of an electrode, and d denotes a gap between electrodes)
In the case of the conventional gyroscope, the change of a gap between a leg and a detection electrode due to vibration, namely the capacitance change due to the change of a gap d between electrodes in the equation (1), is detected. On the other hand, in the case of the gyroscope of the present invention, the change of the facing area between detection electrodes due to vibration, namely the capacitance change due to the change of the electrode area S in the equation (1), is detected.
In detail, in the case of the first gyroscope of the present invention, on the vibration member side, a plurality of detection movable electrodes connected to each other in parallel are provided on the surface parallel to the displacement detection direction of the free end, each of which detection movable electrodes has a width equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction. On the other hand, on the base material side, a plurality of detection fixed electrodes connected to each other in parallel are provided and disposed so as to face to the above-mentioned plurality of detection movable electrodes, each of which detection fixed electrodes has a width equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction. The structure described hereinabove is the most important characteristic of the gyroscope of the first gyroscope of the present invention.
Because of the structure described hereinabove, when the angular velocity round the rotation axis in the longitudinal direction of, the vibration member is entered while the vibration member of the tuning fork is being vibrated by means of a driving means, the vibration in the direction orthogonal to the above-mentioned vibration direction is caused due to Coriolis force. At that time, the detection movable electrodes on the vibration member side is facing to the detection fixed electrodes on the base material side, and the facing area between the detection movable electrodes and the detection fixed electrodes changes concomitantly with vibration of the vibration member, as the result the capacitance change is caused. By detecting the capacitance change, the angular velocity can be detected. The reason why the width of each detection electrode is to be equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction is that the facing area between a detection movable electrode on the vibration member side and a detection fixed electrode on the base material side could become 0 to result in capacitance detection failure when the vibration member received a large angular velocity and the vibration member is vibrated maximum if the width of each detection electrode is smaller than the maximum, amplitude of the vibration member. Herein, the term xe2x80x9camplitudexe2x80x9d only means the amplitude of vibration caused by Coriolis force generated when the angular velocity is entered as it is understood from xe2x80x9camplitude in the displacement detection directionxe2x80x9d, and will not means the amplitude of vibration caused by the driving means.
In detail, in the case of the first gyroscope of the present invention, in which base end portion of the vibration member is supported by an arbitrary base material, the detection fixed electrodes may be disposed on the base material so as to face to the detection movable electrodes of the vibration member, and it is not necessary to provide the detection electrode between legs unlike the conventional gyroscope. As the result, because the gap between legs can be minimized to the working limit of material of the tuning fork such as silicon, the Q-value is increased, the detection sensitivity is improved, and the driving voltage is reduced. As a matter of course, the size of the device can be miniaturized.
As the above-mentioned driving means, for example, driving electrodes may be provided on the vibration member side and the base material side so as to face each other. In this case, the driving electrodes are formed so as to extend in the extension direction of each vibration member, and these electrodes are desirably disposed apart from each other to prevent the parasitic capacitance between the driving electrode and the detection electrode. If the parasitic capacitance is generated between the driving electrode and the detection electrode, then the parasitic capacitance is also detected when the angular velocity is detected and the capacitance change caused between detection electrodes is to be detected, and functions as the noise component to thereby causes reduction of S/N ratio disadvantageously. However, such disadvantage is prevented by disposing the driving electrode and the detection electrode apart from each other.
The detection movable electrodes may be disposed on the top surface or the bottom surface of the vibration member of the tuning fork. In this case, the detection capacitance can be large, and the electrode is formed easily. Furthermore, the detection movable electrodes may be disposed on the end surface in the extension direction of the vibration member. In this case, the detection fixed electrodes can be formed in the same process as that for fabrication of the tuning fork, and the interference between the detection fixed electrodes and the driving means is reduced.
In the case the above-mentioned vibration member is formed of conductive material, the above-mentioned detection movable electrodes are preferably provided with interposition of an insulative film formed on at least on the free end portion of the vibration member.
As for the positional relation between each detection movable electrode and each detection fixed electrode, the end of each detection movable electrode and each corresponding detection fixed electrode are disposed desirably so as to deviate each other in the displacement detection direction of the vibration member by a distance equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction.
The reason is that generally the vibration direction of the vibration member in the direction orthogonal to the driving direction changes depending on the direction of the angular velocity namely clockwise or anti-clockwise when the vibration member receives the angular velocity round the rotation axis in the longitudinal direction. In the case that each detection movable electrode and each corresponding detection fixed electrode are disposed with deviation, when the vibration member is displaced into any one direction, if the change occurs in the direction so as to increase the facing area between each detection movable electrode and each corresponding detection fixed electrode and concomitantly so as to increase the capacitance. On the other hand, when the vibration member is displaced in the reverse direction to the previous direction, the change occurs in the direction so as to decrease the facing area between each detection movable electrode and each corresponding detection fixed electrode and so as to decrease the capacitance without exception. Therefore because the direction of the angular velocity can bee detected by checking positive/negative of the change magnitude of the capacitance, it is preferable to dispose each detection movable electrode and each corresponding detection fixed electrode with deviation. In other words, if the ends of each detection movable electrode and each corresponding detection fixed electrode are disposed without deviation, the facing area between each detection movable electrode and each corresponding detection fixed electrode changes so as to decrease always regardless of the displacement direction of the vibration member, in that case only the absolute value of the angular velocity is detected but the direction of the angular velocity cannot be detected. Furthermore, it is difficult to incorporate each detection movable electrode and each corresponding detection fixed electrode without deviation.
An input apparatus of the present invention is characterized by comprising the first gyroscope of the above-mentioned present invention. By incorporating the gyroscope of the present invention, a small-sized apparatus such as a coordinate input apparatus for a personal computer or the like is realized.
The second gyroscope of the present invention is provided with a vibration member served as a tuning fork, a base material disposed so as to face to the above-mentioned vibration member, a driving means for driving the above-mentioned vibration member, a plurality of detection movable electrodes provided on the surface side parallel to the displacement detection direction of the free end portion of the above-mentioned vibration member, each of which detection movable electrodes has a width equal to or larger than the maximum amplitude of the above-mentioned vibration member in the displacement detection direction, and detection fixed electrodes comprising two electrode groups, each group of which two electrode groups comprises a plurality of electrodes, which electrodes of the above-mentioned two electrode groups are provided on the above-mentioned base material with facing to the above-mentioned plurality of detection movable electrodes so as to form the capacitance respectively with any electrode of the above-mentioned plurality of detection movable electrodes, the outer end of each of which electrodes of the one electrode group out of the above-mentioned two electrode groups is disposed with deviation to the outside from the one outer end of the above-mentioned detection movable electrodes that are facing to the above-mentioned each electrode by a distance equal to or larger than the maximum amplitude of the above-mentioned vibration member in the above-mentioned displacement detection direction, the outer end of each of which electrodes of the other electrode group out of the above-mentioned two electrode groups is disposed with deviation to the outside from the other outer end of the above-mentioned detection movable electrodes that are facing to the above-mentioned each electrode by a distance equal to or larger than the maximum amplitude of the above-mentioned vibration member in the above-mentioned displacement detection direction, and each of which above-mentioned electrodes has a width equal to or larger than the maximum amplitude of the above-mentioned vibration member in the displacement detection direction, wherein the difference between the sum of capacitances formed between the one electrode group out of the above-mentioned detection fixed electrodes and the above-mentioned plurality of detection movable electrodes that are facing to the one electrode group and the sum of capacitances formed between the other electrode group out of the above-mentioned detection fixed electrodes and the above-mentioned plurality of detection movable electrodes that are facing to the other electrode group is detected.
The third gyroscope of the present invention is provided with a vibration member served as a tuning fork, a base material disposed so as to face to the above-mentioned vibration member, a driving means for driving the above-mentioned vibration member, a plurality of detection fixed electrodes provided on the above-mentioned base material so as to face to the surface parallel to the displacement detection direction of the free end portion of the above-mentioned vibration member, each of which detection fixed electrodes has a width equal to or larger than the maximum amplitude of the above-mentioned vibration member in the displacement detection direction, and detection movable electrodes comprising two electrode groups, each of which groups comprises a plurality of electrodes, which electrodes of the above-mentioned two electrodes are disposed on the both sides parallel to the displacement detection direction of the free end portion of the above-mentioned vibration member with facing to any electrode of the above-mentioned plurality of detection fixed electrodes so as to form the capacitance with the above-mentioned plurality of detection fixed electrodes, the outer end of each of which electrodes of the one electrode group out of the above-mentioned two electrode groups is disposed with deviation to the outside from the one outer end of the above-mentioned detection fixed electrodes that are facing to the above-mentioned each electrode by a distance equal to or larger than the maximum amplitude of the above-mentioned vibration member in the above-mentioned displacement detection direction, the outer end of which electrodes of the other electrode group out of the above-mentioned two electrode groups is disposed with deviation to the outside from the other outer end of the above-mentioned detection fixed electrodes that are facing to the above-mentioned each electrode by a distance equal to or larger than the maximum amplitude of the above-mentioned vibration member in the above-mentioned, displacement detection direction, and each of which above-mentioned electrodes has a width equal to or larger than the maximum amplitude of the above-mentioned vibration member in the displacement detection direction, wherein the difference between the sum of capacitances formed between the one electrode group out of the above-mentioned detection movable electrodes and the above-mentioned plurality of detection fixed electrodes that are facing to the one electrode group and the sum of capacitances formed between the other electrode group out of the above-mentioned detection movable electrodes and the above-mentioned plurality of detection fixed electrodes that are facing to the other electrode group is detected.
In detail, the structure of the second gyroscope of the present invention is most characteristic as described herein under. On the vibration member side, a plurality of detection movable electrodes, each of which detection movable electrodes has a width equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction, are provided on the surface of the vibration member parallel to the displacement detection direction of the free end portion. On the other hand, on the base material side, detection fixed electrodes comprising two electrode groups are provided, each electrode of which detection fixed electrodes has a width equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction, each group of which two electrode groups comprises a plurality of electrodes, each electrode of which two electrode groups is disposed with facing to any one of the above-mentioned plurality of detection movable electrodes so as to form a capacitance with any one of the plurality of detection movable electrodes, the outer end of each electrode of the one electrode group of which two electrode groups is disposed so as to deviate outside from the one outer end of each detection movable electrode by a distance equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction, and the outer end of each electrode of the other electrode group of which two electrode groups is disposed so as to deviate outside from the other outer end of each detection movable electrode by a distance equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction.
The, method for detecting the capacitance change is characteristic as described herein under. The difference between the sum of a plurality of capacitances formed between the electrodes of the one electrode group out of two electrode groups comprising a plurality of detection fixed electrodes and a plurality of detection movable electrodes that are facing to the detection fixed electrodes respectively and the sum of a plurality of capacitances formed between the electrodes of the other electrode group out of two electrode groups comprising a plurality of detection fixed electrodes and a plurality of detection movable electrodes that are facing to the detection fixed electrodes respectively is detected.
The structure of the third gyroscope of the present invention is most characteristic as described herein under. On the base material side, a plurality of detection fixed electrodes, each electrode of which detection fixed electrodes has a width equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction, are provided on the surface parallel to the displacement detection direction of the free end of the vibration member. On the other hand, on the vibration member side, detection movable electrodes comprising two electrode groups, each electrode of which detection movable electrodes has a width equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction, each electrode of which two electrode groups is faced to any one of the plurality of detection fixed electrodes so as to form a capacitance with any one of the plurality of detection fixed electrodes, the outer end of each electrode of the one electrode group out of which two electrode groups is disposed with deviation to the outside from the one outer end of each detection fixed electrode by a distance equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction, and the outer end of each electrode of the other electrode group out of which two electrode groups is disposed with deviation to the outside from the other outer end of each detection fixed electrode by a distance equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction.
The method for detecting the capacitance change is characteristic as described herein under. The difference between the sum of a plurality of capacitances formed between the electrodes of the one electrode group out of two electrode groups comprising a plurality of detection movable electrodes and a plurality of detection fixed electrodes that are facing to the detection movable electrodes respectively and the sum of a plurality of capacitances formed between the electrodes of the other electrode group out of two electrode groups comprising a plurality of detection movable electrodes and a plurality of detection fixed electrodes that are facing to the detection movable electrodes respectively is detected. In other words, in the second and third gyroscopes of the present invention, the differential detection method is used for detection of the capacitance change magnitude.
Because the structure as described hereinabove is applied, in the case of the second and third gyroscopes of the present invention, in which base end portion of the vibration member is supported by an arbitrary base material, the detection fixed electrodes may be disposed on the base material so as to face to the detection movable electrodes of the vibration member, and it is not necessary to provide the detection electrode between legs unlike the conventional gyroscope. As the result, because the gap between legs can be minimized up to the working limit of material of the tuning fork such as silicon, the Q-value is increased, the detection sensitivity is improved, and the driving voltage is reduced. As a matter of course, the size of the device can be miniaturized.
Furthermore, in the case of the second and third gyroscope of the present invention, the detection electrode provided on the other side that is facing to the detection electrode provided on any one of the base material side and the vibration member side comprises two electrode groups, the outer end of each electrode of the one electrode group out of the two electrode groups deviates outside from the one outer end of the detection electrode provided on the facing side by a distance equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction, and the outer end of each electrode of the other electrode group deviates outside from the other outer end of the detection electrode provided on the facing side by a distance equal to or larger than the maximum amplitude of the vibration member in the displacement detection direction. Because of the structure as described hereinabove, when the vibration member is displaced in any one direction, if the facing area between each electrode of the one electrode group and the detection electrode that is facing to the electrode of the one electrode group increases and the capacitance increases concomitantly, then the facing area between each electrode of the other electrode group and the detection electrode that is facing to the electrode of the other electrode group decreases and the capacitance decreases concomitantly on the other hand. When the difference between the sum of a plurality of capacitances formed on the one electrode group side out of the two electrode groups comprising detection electrodes and the sum of a plurality of a capacitances formed on the other electrode group side is made, the initial capacitance value is canceled because the initial capacitance values of both sides without displacement are equal to each other, and the capacitance change magnitude of the one side is positive and the capacitance change magnitude of the other side is negative, as the result only the capacitance change magnitude is detected. Therefore, the noise component included in the initial capacitance value is canceled, and the detection accuracy is thereby improved.
Furthermore, in the case of the structure in which the number of electrodes of each electrode group out of the two electrode groups comprising detection electrodes is equal to the number of electrodes of the other detection electrodes, that is, the structure in which each electrode of the two electrode groups forms a pair with one facing detection electrode, the width direction is used most effectively.
As the above-mentioned driving means, for example, driving electrodes may be provided on the vibration member side and the base material side so as to face each other. In this case, the driving electrode is formed extendedly in the extension direction of each vibration member, and these electrodes are disposed desirably apart from each other to prevent the parasitic capacitance between the driving electrode and the detection electrode. If the parasitic capacitance is formed between the driving electrode and the detection electrode, the parasitic capacitance is detected undesirably when the angular velocity is detected and the capacitance change generated between the driving electrode and the detection electrode is detected, the parasitic capacitance functions as the noise component to cause the reduction of S/N ratio disadvantageously. However, if the driving electrode and the detection electrode are disposed apart from each other, such disadvantage is prevented.
The detection side electrode may be provided on the top surface or on the bottom surface of the tuning fork. In this case, the detected capacitance can be large, and the electrode can be formed easily. Otherwise, the detection movable electrode may be disposed on the end surface in the extension direction of the vibration member. In this case, the detection fixed electrode can be formed in the same process as that for forming the tuning fork, and the interference between the detection fixed electrode and the driving means is reduced.
In the case that the above-mentioned vibration member consists of conductive material, the above-mentioned plurality of detection movable electrode or a plurality of pairs of detection movable electrodes are provided preferably with interposition of an insulative film formed at least on the free end portion of the vibration member.
Another input apparatus of the present invention is characterized in that the second and/or third gyroscope of the present invention is incorporated. By using the gyroscope of the present invention, for example, a small-sized apparatus such as a coordinate input apparatus or the like is realized.